I had two encounters over the past two days. 1 was receiving unprotected oral sex and brief anal being the insertive partner (condom was used and partner is on prep, lasted about 10 seconds with no ejaculation).  The other was mutual oral unprotected with a csw and some sex toy play (toys were cleaned). I have been taking amoxicillin the past 2 days since I had it in case (I know this is a bad idea). 3X500 a day. My concern is the STis that are transmitted via oral sex. Would the amoxicillin work to prevent or abort the infection? Both people have assured me they are regular tested and sti free. My anxiety is getting the best of me. I know oral sex is relatively safe but not without risk, should I continue the amoxicillin? I thought about getting doxycycline. 

Welcome to the Forum.  Thanks for your questions.  I'll be glad to comment, focusing on your risk for bacterial STIs from oral sex. By and large, the risk for acquisition of STIs from both giving and receiving oral sex is lower than for other sorts of sexual exposure.  Following receipt of oral sex the most common STIs are gonorrhea, non-gonococcal urethritis due to introduction of normal oral bacteria into the urethras (most experts do not feel that this form of NGU is transmissible to sex partner) and, theoretically although almost never syphilis.  Chlamydia is almost never acquired from receipt of oral sex.  The amoxicillin you are taking would prevent syphilis and likely reduce your risk for NGU.  It is not particularly likely to prevent gonorrhea if exposed.  As for performing oral sex on an infected partner, once again the most likely STI is gonorrhea and very, very rarely, syphilis.  Again the amoxicillin would be expected to prevent syphilis but not necessarily gonorrhea.  I would not be willing to provide you with any antibiotics following this exposure if you were to see me in clinic.  The risk is too low.  Rather I would suggest that, if you are worried (I would not be) to get tested with both a urine test and a throat swab 3-5 days after the encounter.---

Thank you sir. When you say you wouldn’t be worried is that because statistically most people do not have STis and then the risk of transmission on the mentioned activities is low? Is herpes a major risk concern for oral? Like many posters here i am letting my anxiety drive my googling  and research. Of course not engaging in these types of encounters is what I’m m working on not doing. 

Google is NOT your friend here.  Please stay away from it as it will only unnecessarily fuel your anxiety.---

Thank you. I know this will be the last reply. This morning I have had an upset stomach. This of course concerns me but could that be from the 3 days of amoxicillin? Or maybe even stress. I had planned to get an RX for doxycycline but after your response I will attempt to stop worrying. Should I finish the antibiotics as a preventative for a possible infection from the two encounters ?

I suspect your stomach upset is a combination of the amoxicillin and anxiety.  I see no need for additional antibiotics and would stop them now.  ---

Thank you. I will stop taking the amoxicillin.  Based on the encounter do you think I am safe to resume unprotected sex with wife? 

Final response.  Yes, I would be feel comfortable having unprotected sex with your regular sex partner. EWH---